I believe this would just require changing:
https://github.com/yarnpkg/berry/blob/master/packages/yarnpkg-shell/sources/index.ts

The evaluateVariable function already supports a "RANDOM" special case. We would just add another for "PWD" to return process.cwd()

While I don't have a super strong feeling against $PWD, I personally don't find it incredibly useful considering that we already have $(pwd), with pwd being a portable builtin.

I agree that $PWD is not that useful because of the existence of $(pwd) (even though I think we should still add it for better bash compliance), while thinking about this issue $OLDPWD came to my mind which would be useful to have (e.g. IIRC someone needed it for a shared script use case "g:format": "cd $INIT_CWD && prettier --config-path=$OLDPWD", but I didn't remember $OLDPWD existed at that time). What do you think about adding both $PWD and $OLDPWD to the shell?

That sounds reasonable 👍

I'd love to add OLDPWD, however I'm not sure how I'd accomplish that in a non-bash environment? How can I know what the last known working directory was in NodeJS?

@yinzara The shell has a state which contains the cwd, which is only modified by the cd builtin. Because of this, I think that the best option would be to initialize OLDPWD when the shell starts, and then modify it when cd is called. For PWD it's much simpler, as you only have to return state.cwd.

Technically PWD and OLDPWD aren't magical at all (contrary to RANDOM, for instance, which has a special resolution logic) - it's just that they both get set in the env each time you call the cd builtin. For example:

❯ /mnt/c/Users/nison ❯ PWD=lol

❯ /mnt/c/Users/nison ❯ echo $PWD
lol

❯ /mnt/c/Users/nison ❯ cd

❯ /home/arcanis ❯ echo $PWD
/home/arcanis

I could modify the yarn shell to initialize both the OLDPWD and PWD environment variables to process.cwd() when it starts then modify the environment variables in the "cd" builtin.

If I was within the Yarn shell for the entirety of my execution this wouldn't be an issue, however if one of the main use of yarn shell is to execute scripts from a package.json, I would expect that $OLDPWD would work within a script giving me the working directory of the last directory working directory I was in when I executed the package script.

However given the above implementation, if I evaluated echo $OLDPWD in a package.json script, it would actually be the same value as $PWD as I had never executed the cd buildin.

Thoughts?